1. Field of the Invention
This invention relates to circuit breakers and, more particularly, to circuit breakers having a remotely controlled electromagnetic solenoid and functions both as a current limiting circuit breaker and contactor with a single set of contacts that is operated manually, by a bimetal, or by a short circuit trip coil.
2. Description of the Prior Art
Electrical distribution systems have increased in size and capacity to meet expanding requirements for electrical service. Utilities have adopted lower impedance transformers to reduce system power losses, regulation problems, and costs. Even so, the short circuit fault currents available to plague distribution systems continue to increase, reaching as high as 200,000 A. To prevent these high available fault currents from damaging electrical distribution systems, protective devices limiting the perspective let-through currents are required. Fuses and, more recently, current limiting circuit breakers, have been used successfully to limit these fault currents. They can reduce, to tolerable levels, both the peak fault currents (I.sub.p) and thermal energy (I.sup.2 t) that reach downstream equipment. Mechanical and magnetic forces that can destroy equipment are proportional to the square of the peak currents (I.sub.p).sup.2, and thermal damage is proportional to the energy let-through (I.sup.2 t).
The use of low impedance transformers and interconnected networks of low voltage AC power distribution systems results in large short circuit currents. Fault currents in excess of 100 KA are common. Traditionally, high fault current prediction has been provided in current limiting fuses in conjunction with circuit breakers. However, a new generation of high speed electromagnetically driven, single, and multiple circuit breaker limiting devices have been developed. These devices not only perform the function of a current breaker and current limiting fuse, but are also resettable and reusable. These devices can also be effectively applied to motor control as well as power distribution systems.
Such distribution systems are increasingly adopting automated distribution means which are powered from the distribution secondary circuits and are designed to control and monitor the status of capacitor banks, protective devices, current switches, and distribution transformers connected to primary circuits of the distribution system.
A disadvantage of some prior circuit breakers has involved the safety of personnel. Some prior circuit breakers could be actuated by remote control to an "on" or closed circuit connection, even through the breaker had been previously tripped to an open circuit by a person on-site for some purpose such as maintenance.